This invention relates to tufting machines, and more particularly to a tufting machine having an adjustable needle stroke mechanism for adjusting the stroke of all the push rods and thus the needles from each end of the machine.
Needle stroke adjusting mechanisms for tufting machines are of two general types. In one type, known as a "dial type" adjustment of the stroke of the tufting machine is made by changing the point of attachment of an input drive to a rocker arm through which an oscillatory motion from an eccentric cam mounted on a rotating shaft is applied to a rocker type or oscillating main shaft, the needles being reciprocably driven by push rods connected to respective rocker arms clamped above the push rods to the main shaft. Mechanisms of this type are well known in the art, examples being illustrated in U.S. Pat. Nos. 2,977,905 and 3,881,432. In the other type of needle stroke adjusting mechanism the connecting rod of an eccentric or crank arrangement is mounted directly to each push rod, the eccentric or other arrangement being mounted on a rotating main shaft. Again, mechanism of this type are now well known in the art, and examples are illustrated in U.S. Pat. Nos. 3,839,972; 3,857,345 and 4,515,096.
In tufting machines having the latter type adjusting mechanisms, since there is an adjusting mechanism at each push rod, and in most full size tufting machines (12 to 15 feet) there may anywhere from 8 to 12 push rods, the substantially greater number of parts creates a more expensive tufting machine and thus these mechanisms are generally used only for specialized and very high speed machines. However, the main disadvantage of these mechanisms is that each time a needle stroke adjustment is required to be made, since the adjustments must be made at each push rod which is internal of the tufting machine head, the head of the machine must be opened and all the mechanisms must be substantially disassembled for such changes to be performed. This procedure is extremely time consuming and results in large machine down-time.
In "dial type" adjusting mechanism tufting machines, needle stroke changes need be performed only at each end of the machine by moving the point of attachment from the input drive to the rocker arm, the rocker arm having an arcuate slot with a center of curvature coinciding with the geometric center of the eccentric cam when the cam is at bottom dead center. Since there are only two such mechanisms and since there is no need to enter the interior of the machine head and tear down substantial portions thereof, the amount of time consumed when making a needle stroke change in such machines is substantially less than with the non-dial type machine. Thus, dial type machines are widely used in those tufting machines which are not in the very high speed range.
However, dial type machines do have inherent disadvantages. Firstly, the connection between the drive input and the rocker arm must be such that it will satisfactorily transmit a drive to the rocker shaft without slippage of the connection yet lend itself to adjustment between a range of separate and distinct positions. A second problem concerns the nonuniform nature of the forces applied to the needle mechanism arising from the change in leverage of the slotted rocker arm upon adjustment. A third problem is that the slotted rocker arm is inherently structurally weak and intolerant of the forces transmitted by high speed tufting machines. A still further disadvantage of such structures is the possible need for compensatory adjustment of other tuft-forming instrumentalities of the tufting machine on needle stroke adjustment as of the bottom dead center position of the needle in like circumstances.